Some of conventional ejectors disclosed in, for example, Patent Documents 1 and 2 have been known. The ejector of this type includes a nozzle part that depressurizes a refrigerant condensed and liquefied by a refrigerant condenser after compressed to a high pressure by a compressor when the ejector is used in a refrigeration cycle, a suction part that draws a lower-pressure-side refrigerant flowing out of a refrigerant evaporator, and a diffuser part that mixes the refrigerant jetted from the nozzle part with the refrigerant drawn from the suction part and increases a pressure of the mixture.
Further, the nozzle part of the ejector in Patent Document 1 includes a first nozzle that depressurizes and expands a liquid refrigerant which flows therein from the refrigerant condenser, and a second nozzle that again depressurizes and expands the refrigerant that has been put into two phases of gas-liquid by the first nozzle, and ejects the refrigerant. With the above configuration, the refrigerant is expanded into the two phases of gas-liquid by the first nozzle, and further depressurized and expanded by the second nozzle. As a result, an exit velocity of the refrigerant that flows out of the second nozzle can be increased, and nozzle efficiency can be improved.
Also, in the general ejector, a diffuser part (pressurizing part) is coaxially arranged on an extension in an axial direction of the nozzle part. Further, Patent Document 2 discloses that a spread angle of the diffuser part thus arranged is relatively reduced so that ejector efficiency can be improved. The nozzle efficiency means energy conversion efficiency when a pressure energy of the refrigerant is converted into a kinetic energy in the nozzle part. The ejector efficiency means energy conversion efficiency as the overall ejector.
However, in the ejector of Patent Document 1, for example, when a refrigerant pressure difference between a high pressure side and a low pressure side is small in a low load of the refrigeration cycle, most of the refrigerant pressure difference is depressurized by the first nozzle, and the refrigerant can be hardly depressurized in the second nozzle. As a result, in the low load of the refrigeration cycle, the refrigerant may not be sufficiently pressurized in the diffuser part. That is, in the ejector of Patent Document 1, the sufficient operation of the ejector which matches the load of the refrigeration cycle may not be obtained.
On the contrary, when the diffuser part having the relatively small spread angle disclosed in Patent Document 2 may be applied to the ejector of Patent Document 1, to thereby improve the ejector efficiency and pressurize the refrigerant sufficiently in the diffuser part in the low load of the refrigeration cycle. However, when the diffuser part of this type is applied, a length of the nozzle part in the axial direction becomes longer as a whole of the ejector, resulting in a risk that a body of the ejector becomes unnecessarily longer in the normal load of the refrigeration cycle.